PC-NRLF 


EXCHANGE 


Thermal  Reactions  in  Carbureting 
Water  Gas 


DISSERTATION 


SUBMITTED  IN  PARTIAL  FULFILLMENT  OF  THE  REQUIREMENTS 

FOR  THE  DEGREE  OF  DOCTOR  OF  PHILOSOPHY 

IN  THE  FACULTY  OF  PURE  SCIENCE 

COLUMBIA  UNIVERSITY 


BY 
Walter  Frank  Rittman,  M.A.,  M.E. 


NEW  YORK  CITY 
1914 


Thermal  Reactions  in  Carbureting 
Water  Gas 


DISSERTATION 


SUBMITTED  IN  PARTIAL  FULFILLMENT  OF  THE  REQUIREMENTS 

FOR  THE  DEGREE  OF  DOCTOR  OF  PHILOSOPHY 

IN  THE  FACULTY  OF  PURE  SCIENCE 

COLUMBIA  UNIVERSITY 


BY 
Walter  Frank  Rittman,  M.A.,  M.E. 

NEW  YORK  CITY 
1914 


ESCHENBACH  PRINTING  COMPANY 
EASTON,  PENNA. 
1914 


- 


To  GELLERT  ALLEMAN 

PROFESSOR   OF    CHEMISTRY 
SWARTHMORE    COLLEGE 


305647 


ACKNOWLEDGMENTS 

The  author  wishes  to  express  his  sincere  apprecia- 
tion to  Professor  Milton  C.  Whitaker,  at  whose  sug- 
gestion and  under  whose  direct  supervision  this  work 
was  carried  out;  his  practical  advice  and  active  co- 
operation have  -been  essential  factors  in  the  progress 
and  development  of  this  research. 

Thanks  are  due  to  Professor  J.  L.  R.  Morgan  for 
assistance  in  the  development  of  the  theoretical  dis- 
cussion; to  Professor  F.  J.  Metzger  for  suggestions  as 
to  methods  of  gas  analysis  and  experimental  pro- 
cedure; and  to  the  other  members  of  the  chemical 
faculty  for  time  given  to  informal  discussions  of 
the  principles  involved  in  the  problem. 

W.    F.    RlTTMAN 
CHEMICAL  ENGINEERING  LABORATORY 
COLUMBIA  UNIVERSITY,  NEW  YORK 
May.  1914 


THERMAL  REACTIONS  IN   CARBURETING  WATER  GAS 


PART  I— THEORETICAL 

Much  careful  scientific  work  has  been  done  on  the 
equilibria  involved  in  the  manufacture  of  uncarbureted 
blue  water  gas.  In  the  combined  processes  of  manu- 
facturing and  carbureting  blue  water  gas  according 
to  present  practice,  few  experiments  have  been  made 
on  the  equilibria  of  the  constituents  to  find  out  the 
effect  of  varying  pressure,  temperature  and  concen- 
tration conditions.  In  the  technical  literature  of  gas 
manufacture,  one  rarely  finds  a  reference  to  the  rela- 
tionship which  may  exist  between  the  spheres  of  re- 
action in  the  process.  The  natural  conclusion  has 
been  that  the  water  gas  and  oil  gas  reactions  are  sepa- 
rate and  influence  each  other  but  little. 

It  is  proposed  to  consider  some  of  the  factors  in 
which  the  H2,  CO,  CO2  and  H2O  of  the  blue  water  gas 
may  affect  the  proportions  of  CH4,  C2He,  C2H4,  H2, 
etc.,  resulting  from  the  cracking  of  the  gas  oil  which 
is  added.  Likewise  the  influence  of  the  gases  coming 
from  the  oil  on  the  percentage  composition  of  the  final 
gas  mixture  will  be  considered. 

When  the  blue  water  gas  or  oil  gas  are  manufac- 
tured in  separate  operations,  hydrogen  is  the  only 
gas  which  is  found  in  the  free  state,  in  any  quantity. 
But  if  the  two  gases,  separately  made,  should  be  brought 
together  at  high  temperature  in  a  container  such  as  a 
gas  plant  superheater,  would  there  not  be  new  equi- 
libria to  be  satisfied?  For  example,  might  not  the  CO 
and  Ho  of  one  become  CH4  and  H2O  of  the  other,  or 
vice  versa?  In  case  of  these  new  equilibria,  of  course, 
there  would  be  vital  reactions  between  the  gases  of  the 
two  processes.  In  actual  manufacturing  practice, 
all  the  gases  produced  are  in  intimate  contact  at  high 
temperature  for  the  greater  part  of  the  manufacturing 
period,  i.  e.,  while  passing  through  the  carbureter  and 
superheater.  Is  it  then  correct  to  regard  carbureted 
water  gas  as  the  result  of  two  distinct  reactions? 

Equilibrium  conditions  tend  to  establish  them- 
selves both  during  the  periods  of  initial  cracking  of 
the  oil  and  the  subsequent  passage  of  the  mixture 
through  the  carbureter  and  superheater.  Gas  oil 
itself  can  be  "cracked"  in  a  short  distance,  as  has 

d) 


been  shown  in  practically  all  laboratory  experiments; 
in  the  laboratory  the  length  of  the  cracking  tube  is 
usually  a  question  of  inches.  It  would  seem  on 
a  priori  grounds  that  the  only  important  reason  for 
the  existence  of  the  superheater  is  to  enable  the  various 
gases  present  to  interact  ("fix")  and  reach  a  favora- 
ble equilibrium. 

This  laboratory  has  begun  a  comprehensive  study 
of  the  reactions  and  equilibria  involved  in  water  gas 
manufacture.  While  unable  to  cover  the  field  in  two 
years,  it  has  come  to  a  full  realization  of  the  impor- 
tance of  the  investigation.  The  present  paper  will 
be  confined  to  a  theoretical  consideration  of  the  prob- 
lem. Further  papers  will  take  up  experimental  data. 

The  problem  has  been  attacked  entirely  from  the 
point  of  view  of  physical  chemistry,  and  from  the 
standpoint  of  mass  action  and  thermodynamics. 
In  so  doing,  the  mechanism  of  the  reactions  involved 
has  not  been  seriously  considered.  The  materials 
at  the  start,  the  final  products  desired,  the  energy 
transformations  essential  to  bring  the  latter  from  the 
former,  the  temperature,  the  pressure  and  the  concen- 
tration conditions  favorable  to  the  changes  haVe  had 
primary  consideration. 

Basing  an  experimental  investigation  upon  the 
theoretical  considerations  evolved,  it  has  been  possible, 
among  other  things,  to  establish  the  following  results: 

(1)  Increase  the  yield  of  illuminants  over  the  best 
results  recorded   in  the  literature   by   more  than    100 
per  cent. 

(2)  Decrease    the    carbon    deposited    to    less    than 
i  per  cent,  by  weight,  of  the  oil  used. 

(3)  Make  an  oil  gas  in  which  56  per  cent  of  the  fixed 
gases  are  illuminants. 

These  figures  result  from  the  application  of  condi- 
tions which  the  theory  shows  would  favor  such  results 
more  than  do  those  at  present  used  in  water  gas  manu- 
facture. Conversely  by  applying  conditions,  which, 
according  to  theory  would  give  less  favorable  results 
to  the  theory  involved,  and  by  comparing  the  maximum 
yield  under  these  conditions  with  a  maximum  yield 
obtained  under  ordinary  conditions,  it  has  been  found 
possible  to: 

(4)  Decrease  the  yield  of  illuminants  by  25  per  cent. 

(5)  Increase  the  carbon  deposited  to  51.5  per  cent, 
by  weight,  of  the  oil  used. 

(6)  Make    an    oil    gas    containing    only    5    per   cent 
total  illuminants. 

(2) 


Further,  it  has  been  found  possible  to  produce: 

(7)  A   viscous  tar  of  relatively  high  specific  gravity 
containing  naphthalene  and  anthracene;  or 

(8)  A  liquid  "tar"  of  relatively  low  specific  gravity 
resembling  petroleum  oil,  and  containing  no  naphtha- 
lene and  anthracene. 

In  the  examination  of  the  problem,  no  single  reaction 
can  be  considered  exclusively  by  itself.  All  the  reactions 
are  vitally  interrelated,  though  any  single  reaction, 
or  set  of  reactions,  may  be  extremely  important  as 
indicating  a  tendency.  The  experiments  are  designed 
to  obtain  the  largest  yield  of  hydrocarbons,  and  to 
eliminate,  as  much  as  possible,  CO2,  water  vapor, 
deposited  carbon,  and  tar  vapors.  The  goal  is  to  in- 
crease the  yield  of  illuminants. 

MANUFACTURE  OF  UNCARBURETED  BLUE  WATER  GAS 

The  manufacture  of  blue  water  gas  may  be  repre- 
sented by  the  equations: 

C  +  H20     =  CO    4-     H2  —  29,300  cal.          (i) 
C  -f  2H2O   =  C02  4-  2H2  —  19,000  cal.         (2) 
The    two    equations    are    combined    by    subtracting 
(2)  from  (i)  in  order  to  eliminate  the  carbon: 
CO2  +  H2  =  CO  4-  H2O  —  10,300  cal. 
Equilibrium     is    established     between    these     gases 
when 


where  K  represents  the  usual  equilibrium  constant; 
i.  e.,  the  value  of  the  product  of  the  partial  pressures 
of  CO  and  H20  divided  by  the  product  of  the  partial 
pressures  of  CO2  and  H2.  K  has  a  definite  value  for 
each  definite  absolute  temperature. 

For  a  practical  illustration  of  the  significance  of  equilibrium 
conditions  in  the  manufacture  of  blue  water  gas,  assume  a  theo- 
retically ideal  mixture  consisting  of  50  per  cent  H2  and  50  per 
cent  CO.  Pass  the  two  gases  through  a  chamber  heated  to  715  ° 
C.  (1319°  F.)  until  they  reach  the  equilibrium  of  this  tempera- 
ture; what  are  the  resulting  gases?  K  at  this  temperature  is 
in  the  neighborhood  of  0.30. 

3CO  4-  H2  =  C02  4-  H20  +  2C  4-  68900  cal. 
Under  equilibrium  conditions  at  atmospheric  pressure 

Let  X  -  volume  COz 
then  X  =  volume  H2O 
0.5—    X  =  volume  Hz 
0.5  —  3X  =  volume  CO 


—  2X  =  total  final  volume 
(3) 


(1  _  2X) 


1   =  partial  pressure  QO-i          ~~T«J  l  =  partial  pressure  H2 


)1   =  partial  pressure  H2O    (  -j-£I—  )  1  =  partial  pressure  CO 


M  — 2X/M  —  2X/ 
/0.5  —  3X\»/0.5  —  Xx     •     (0.5  —  3X)3 
V   1  —  2X  }  \  1  —  2X  / 


2XH1  —  2X) 


Solving,  X  =  0.069  =  6.9  per  cent 
2X  =  gas  lost  in  reaction  =   13.8  per  cent 


0.069 


»-<-<«> 


Applying  the  above  calculations  to  a  mixture  of 
1,000  cu.  ft.  each  of  carbon  monoxide  and  hydrogen, 
and  assuming  that  no  hydrocarbons  are  formed, 
there  would  be  a  net  loss  of  13.8  per  cent  (276  cu.  ft.) 
due  to  the  reaction,  leaving  1,724  cu.  ft.  of  mixed  gases, 
as  follows: 

1724  X  0.08  =  138  cu.  ft.  CO2 
1724  X  0.08  =  138  cu.  ft.  H2O 
1724  X  0.34  =  586  cu.  ft.  CO 
1724  X  0.50  =  862  cu.  ft.  H2 

The  water  in  condensing  leaves  a  net  volume  of  permanent 
gases  equal  to  1724  —  138  =  1586  cu.  ft.  This  permanent  gas 
is  composed  of  8.7  per  cent  CO2,  37  per  cent  CO  and  54.3  per 
cent  H2.  ThEre  would  be  also  a  deposit  of  9.25  pounds  of  car- 
bon. In  other  words,  there  are  only  1586  —  138  =  1448  cu. 
ft.  of  the  original  H2  and  CO  remaining. 

Different  temperature  conditions  would  obviously 
give  different  results.  A  numerical  problem  of  this 
nature  shows  how  vitally  equilibria  conditions  influ- 
ence gas  manufacture,  and  indicates  the  commercial 
importance  of  an  understanding  of  such  equilibria 
conditions.  Just  as  the  equilibria  conditions  here 
are  of  importance,  it  can  be  shown  that  they  are  no 
less  important  when  the  reactions  are  between  CO, 
H2,  CO2,  and  H2O  coming  from  the  blue  water  gas 
on  one  hand,  and  H2,  CH4,  C2H6,  C2H4,  and  tar  vapors, 
etc.,  coming  from  the  gas  oil  on  the  other  hand. 

The  blue  water  gas  reactions  and  equilibria  have  been 
investigated1  and  are  well  understood,  so  that  we  know 

i  Bureau  of  Mines,  Bulletin  7,  1911;  Juptner,  Chem.  Ztg.,  1904, 
p.  902;  K.  Neuman,  Stahl  und  Eisen,  1913,  p.  394;  O.  Hahn,  Z.  physik. 
Chem.,  44,  513-547;  C.  LeChatelier  and  K.  Neuman,  Stahl  und  Eisen. 
1913,  p.  1485;  E-  A.  Allcut.  Engineering,  1911,  p.  601. 

(4) 


what  conditions  are  favorable  and  what  are  unfavora- 
ble; i.  e.,  degree  of  temperature,  quantity  of  steam, 
depth  of  fuel  bed,  etc. 

MANUFACTURE    OF    STRAIGHT    OIL    GAS 

The  manufacture  of  an  oil  gas  as  carried  out  by 
the  Pintsch  or  Blau  Gas  companies  is  an  old  process, 
but  is  not  as  well  understood  as  the  blue  water  gas 
equilibrium.  Few  experimental  equilibria  of  the 
various  components  of  oil  gas  have  been  worked  out, 
as  have  been  the  CO2,  CO,  H20  and  H2  relations  of 
blue  water  gas.  Here,  one  at  once  faces  the  fact 
that  in  the  oil  cracking  process,  instead  of  the  four 
gases  of  the  blue  water  gas  reaction,  there  are  all 
the  members  of  the  methane,  ethylene  and  acetylene 
series,  as  well  as  those  hydrocarbons  which  consti- 
tute the  tars  produced  in  pyrogenetic  decomposition. 

Synthetic  methane  has  been  made  from  carbon 
and  hydrogen,1  where  equilibrium  exists  when 


Similarly,  we  may  conclude  that  equilibrium  exists 
between  H2  and  all  of  the  other  hydrocarbons. 

By  combining  the  ethane  and  ethylene  equations 
through  the  elimination  of  carbon,  one  gets  C2H6  = 
C2H4  -f-  H2,  where  equilibrium  conditions  prevail 
when 


For  a  practical  illustration  of  the  meaning  of  this  ex- 
pression, take  the  effect  of  heat  on  a  known  volume  of 
C2H6.  Eliminating  other  reactions  than  the  one  between 
ethane  and  ethylene,  consider  the  resultant  relative 
quantities  of  H2,  C2H6  and  C2H4  at  a  temperature  of 
900°  C.,  taking  the  value  of  K  equal  to  i.  28. 

C2He  =  C2H4  -\-  H2 

Let  X  =  volume  H2 
then  X  =  volume  C2H4 
1  —  X  =  volume  C2H6 


1   +  X  =  total  final  volume 


=  partial  pressure  C2H* 


—  =  partial  pressure 
X  1   -p  X 

.        =  partial  pressure  H2 
1    ~t~   .X. 

1  Pring  and  Fairlie,  Report  of  Eighth  International  Congress;  Ipatiew, 
Jour,  prakl.  Chem.,  1913,  pp.  479-487;  Pring  and  Fairlie,  Jour.  Ghent.  Soc., 
1906  p.  1591;  Ibid.,  1911,  p.  1796;  Ibid.,  1912,  pp.  91-103;  Bone  and 
Coward,  J.  Chem.  Soc.,  1908,  p.  1975.  Proc.  Chem.  Soc.,  1910,  p.  146. 

(5) 


j,  M_+x'M  +  x'         x* 

A.    =    1.20    = _ - 


Solving,  X  =  0.75 

~^=  42.85percentC2H4,         ^-5  =  42.85  per  cent  Hz 

and    -1--  =  14.30  per  cent  CzH6. 

In  dealing  with  any  of  these  equilibria  expressions, 
one  must  be  careful  to  remember  that  no  single  equi- 
librium can  be  considered  by  itself.  In  the  ethane- 
hydrogen-ethylene  equilibrium  at  900°  C.,  for  instance, 
there  is  a  pronounced  tendency  for  the  ethane  to  go 
to  ethylene;  and  in  practice  one  should  expect, 
therefore,  a  high  ethylene  yield,  but  by  referring  to  the 
ethylene— benzene  system  one  finds  that  at  900°  C. 
there  is  an  even  greater  tendency  for  the  ethylene  to 
be  removed  by  polymerization  to  benzene.  Assuming  a 
volume  of  C2H4  and  bringing  it  to  equilibrium  at  900°  C., 
observe  the  resultant  relative  quantities  of  C2H4  and 
C6H«: 

3C2H4   =  CeH6  +  3H2  -f  32500  cal. 

Under  equilibrium  conditions  at  atmospheric  pressure 

X  =  volume  CeHe 
3X  =  volume  H2 
1  —  3X  =  volume  C2H4 


X  =  total  final  volume 


2£ 

=  partial  pressure  of  CeHe 

=  partial  pressure  C2H4 

=  partial  pressure  of  H2 

1  ~r  X 

v  ^"V"          3 

K        Pcsnt  P3Hj  M  +  X    M  +  X' 

K  =  -—, =  68  X   10»  = — — -    (. 


Solving,  X  =  0.33 

°.  '  H  =  24 . 8  per  cent  C6H6,       ^^  =  74 . 4  per  cent  H2 
1  .  o<5  1  .  33 

and   J*?J   =  0.8  per  cent  C2H4. 

Thus  an  experimental  test,  with  the  yield  calculated 
according  to  the  first  equilibrium  without  a  consideration 
of  the  second,  would  result  in  disappointment. 
Further,  not  only  must  the  ethane-hydrogen-ethylene- 
benzene  equilibrium  be  satisfied,  but  each  of  these  con- 
stituents, in  turn,  must  be  in  equilibrium  with  methane, 
acetylene,  propane,  naphthalene,  etc.  In  short,  there 
will  be  a  grand  symphony  of  equilibria  between 
all  components  of  the  system. 

(6) 


Equilibria  expressions,  such  as  the  ones  just  given, 
are  therefore  of  value  when  properly  understood  and 
used  as  a  basis  for  experimental  proof.  First  of  all, 
the  time  element  is  very  important  to  insure  final  equi- 
librium; and  secondly,  their  mathematical  derivations 
involve  integration  factors  based  on  physical  proper- 
ties such  as  specific  heat,  vapor  pressure,  heat  of  reac- 
tion, etc.,  under  conditions  which  have  not  been 
experimentally  determined.  Experimental  demonstra- 
tion based  upon  a  few  selected  and  isolated  equilibria 
is  almost  certain  to  result  in  failure,  due  to  overlooking 
other  equally  important  equilibria  which  might  modify 
or  even  reverse  the  direction  of  final  reactions. 

Sufficient  experimental  and  commercial  work  has 
been  done  on  the  making  of  all  oil  gas  under  atmospheric 
conditions1  to  give  empirical  data  indicating  that  as 
the  temperature  goes  above  800°  C.  the  yield  of 
hydrocarbons  rapidly  decreases;  on  the  other  hand, 
the  hydrogen  and  carbon  rapidly  increase. 

CARBURETED    WATER    GAS    PROCESS 

In  the  carbureted  water  gas  practice,  as  carried  out 
to-day,  there  is  a  combination  of  the  blue  water  gas 
and  the  oil  gas  process.  Much  is  known  about  the 
blue  gas;  it  is  also  known  that  this  blue  gas  is  carbureted 
by  spraying  in  and  cracking  oil  which  furnishes  the 
hydrocarbons  and  illuminants.  There  is  little  scien- 
tific information,  however,  regarding  the  interactions 
and  equilibria  which  are  reached  when  the  two  processes 
are  combined.  The  formation  of  hydrocarbons  and 
water  from  CO  and  H2  or  from  CO2  and  H2  is  not  theo- 
retical speculation;2  likewise  the  destruction  of  hydro- 
carbons with  water  to  form  CO  and  H2  or  CO2  and  H2, 
as  carried  out  in  the  all  oil  water  gas  process,  is  not 
theoretical  speculation.  Whichever  course  prevails 
depends  entirely  upon  conditions.  Consequently,  one 
is  justified  in  concluding  that  the  present  composi- 

1  Haber  and  co-workers,  Jour.  Gasb..   189$,    pp.    377,  395,  435,   452; 
Hempel,  Dissertation.  Jour.  Gasb.,  1910,  pp.  53,  77,  101,  137,  155. 

2  Mayer,  Henseling  and  Altmayer.  J.  f.  Gasb.,  1909,  pp.  166,  194,  238, 
326;   P.  Sabatier,  Chem.  Ztg.,  1913,  p.  148;   P.  Sabatier,  Fr.  Patent  355,325, 
1905;   Ibid.,   355,900,   1905;   Ibid..   361,616;  Ibid.,    400,656;   Eng.    Patent 
14,971,  1908;  Ibid.,  27,045;     L.  Vignon,  Fr.  Patent  416,699,  1909;  Compt. 
rend.,  1913,  pp.  131-134;     Gautier, /&»</.,  1910,  p.    1565;  Elsworthy  and  Wil- 
liamson, Eng.  Patent  12,461,  1902;      Bedford  and  Williams,  Eng.  Patents 
17,017,  22,219,  1909;    H.  J.  Coleman,  Jour.  Gas  Lighting,  1908,  p.  683;     E. 
Erdman,  Jour.f.  Gasb.,  1911,  pp.  737-743;  E.  Orlow,  Jour.  Russ.  Phys.  Chem., 
1908,  p.  1588;     P.  Jockum,  Jour.f.  Gasb.,  1914,  pp.  73,  103,  124,  149;  T.  Hoi- 
gate,  Gas  World,  1914,  p.  90;     German  Patents    183.412.    190,201,     191,026, 
237,499,  226,942,  177,703,  174,343  and  250,909. 

(7) 


tion  of  carbureted  water  gas  is  not  the  result  of  addi- 
tive processes.  Instead  there  is  a  mixture  of  blue 
water  gas  and  cracked  oil  gas  passing  through  the 
carbureter  and  superheater  which  constitute  a  sin- 
gle unbalanced  system  of  gases;  naturally,  there  is  a 
tendency  to  establish  equilibrium  between  the  con- 
stituents just  as  surely  as  there  is  a  tendency  to  estab- 
lish an  equilibrium  between  the  constituents  of  either 
the  blue  gas  or  the  all  oil  gas  when  made  individually. 
This  equilibrium  at  the  usual  temperature  of  the  super- 
heater has  fortunately  favored  the  formation,  or  at 
least  the  preservation,  of  hydrocarbons.  This  fact, 
however,  does  not  prove  that  the  process  is  working 
under  conditions  of,  or  approaching  maximum  effi- 
ciency. Nor  does  it  prove  that  the  present  method 
of  carbureting  water  gas  is  the  most  economical  from 
the  side  of  the  quantity  of  gas  oil  consumed. 

Many  questions  arise  at  this  point.  It  might  be 
possible  to  alter  conditions  in  such  a  way  as  to  solve, 
or  assist  in  solving,  the  naphthalene  and  carbon  prob- 
lems of  the  gas  manufacturer.  It  might  still  further 
be  worth  while  to  question  the  soundness  of  the  natural 
tendency  of  the  American  manufacturer  to  combine 
processes;  it  may  appear  that  the  attempt  to  do  every- 
thing in  a  single  vat  rather  than  carry  it  out  in  stages 
is  not  the  most  economical  method  in  the  end. 

EQUATIONS    AND    THEORETICAL    EQUILIBRIA    INVOLVED 

The  formation  of  methane  from  carbon  monoxide 
and  hydrogen,  or  from  carbon  dioxide  and  hydrogen 
is  an  exothermic  reaction  and  consequently  is 
favored  'by  low  temperatures,  although  at  these  low  tem- 
peratures a  greater  amount  of  time  is  required  for  com- 
plete reaction.  The  rate  of  the  reaction  may  be  greatly 
stimulated  by  catalytic  agents  such  as  nickel  and  cobalt. 
In  view  of  the  fact  that  there  is  a  decrease  in  volume, 
one  should  expect  pressure  to  be  favorable  to  hydro- 
carbon formation.  Equilibrium  exists  between  CO 
and  H2  or  C02  and  H2  on  the  one  side  and  CH4  and 
H2O  on  the  other. 

CO    +  3H2  -  CH4  +     H20  +  48,200  cal. 
CO2  -f-  4H2  =  CH4  +  2H20  +  37,900  cal. 

with  equilibrium  established  when 
~          Pco  PS 

-    ~ 


(8) 


Combining  the  two  equations  with  elimination  of  H2O, 
2CO  -f  2H2  =  CH4  +  C02  +  58,500  cal. 

K" 


Pen* 

In  like  manner  the  equilibria  between  CO,  C02,  and 
H2O,  on  the  one  side,  and  C2H4,  C2H2  and  H2O  on  the 
other,  are  considered  below: 

C2H4  +  2H20  =  2CO    +  4H2—  44,000  cal. 
C2H4  +  4H20  =  2CO2  +  6H2—  23,400  cal. 
C2H2  +  2H20  =  2CO    +  3H2—  500  cal. 
C2H2  +  4H2O  =  2C02  +  5H2—  20,100  cal. 
C2H4  +  2CO2   =  4CO    +  2H2—  64,600  cal. 
C2H2  +  2CO2    =  4CO    +    H2—  21,  100  cal. 
With  these  there  is  sufficient  data  to  determine  in  a 
qualitative  way  the  concentration  conditions  favorable 
to  the  methane,  ethylene  and  acetylene  desired  in   the 
resultant  gas. 

TABLE  I  —  QUALITATIVE  STUDY  OF  EQUILIBRIA 

A 

CH4  +  H2O    v    *    CO  +  3H2 
co  X 


CH4  X  H2Q^ 

CiH4  4-  2H,Q"^~*>   2CO  +  4Ht 
K  =    (CO)2  X  (H2)4 
C2H4  X  (H»0)2 

C2H2  +  2H20  "7~^   2CO  +  3H2 
K  =    (C°)2  X  (H2)» 
CiH«  X  (H2O)z 
FAVORABLE  WHEN  CO  AND  H2  ARE  LARGE  AND  H2O  is  SMALL 

B 

CH4  +  2H20  7"^  COi  +  4H2 
K  =     c°2  X  (H2)« 
CH4  X  (H»0)2 

C2H4  +  4H20  "T"**  2C02  +  6H2 
K  =  (CQ2)2  X  (H2)« 
C2H4  X  (HzO)« 

C2H2  +  4H2O          *    2CO2  +  5H2 
K  =  (co*)2  X   (H2)s 
=  CiHj  X    (H»0)4 
FAVORABLE  WHEN  CO2  AND  H2  ARE  LARGE  AND  H2O  is  SMALL 

C 

CH4  +  CO2    ^    ^    2CO  +  2H2 
=  (CO)  ^  X  (H2)2 
C02  X  CH4 

C2H4  +  2CO2    ^    ^    4CO  +  2H2 
=    (C0)«  X  (Hi)« 
CjH4  X  (CO*)* 

CH2  +  2CO2    ^    ^    4CO  +  H2 
X  H2 


X  (CO2)« 
FAVORABLE  WHEN  CO  AND  H2  ARE  LARGE  AND  CO2  is  SMALL 

(9) 


The  original  complex  state  of  affairs  is  thus  partially 
simplified.  One  sees  that  conditions  favorable  to  the 
formation  of  hydrocarbons,  or  at  least  unfavorable 
to  the  decomposition  of  hydrocarbons,  exist  when  in 

A,  B  and  C  there  is  an  excess  of  H2, 
A  and  C,  there  is  an  excess  of  CO, 

A  and  B,  there  is  a  minimum  of  water  vapor, 

B,  there  is  an  excess  of  CO2, 

C,  there  is  a  minimum  of  CO2. 

An  excess  of  hydrogen  is  favorable  under  any  condi- 
tions; a  minimum  of  water  vapor  is  favorable  under 
any  conditions;  an  excess  of  CO  appears  to  be  favora- 
ble under  any  conditions;  in  the  case  of  CO2,  however, 
one  condition  indicates  an  excess  as  favorable  whereas 
another  indicates  an  excess  as  unfavorable. 

INFLUENCE    OF    TEMPERATURE    ON    EQUILIBRIUM    CONDI- 
TIONS 

While  these  qualitative  relations  are  extremely 
valuable  in  the  consideration  of  favorable  conditions, 
they  do  not  give  a  sufficiently  concrete  idea  of  the 
conditions  which  prevail  at  different  temperatures. 
Each  equilibrium  constant  has  a  definite  value  for  a 
definite  temperature.  If  this  value  of  K  is  considered 
for  500°  C.  the  reaction  may  proceed  in  one  direction; 
whereas  on  considering  the  value  of  K'  for  the  same 
reacting  agents  at  900°  C.,  the  reaction  may  proceed 
in  the  opposite  direction.  Qualitative  expressions 
point  merely  in  general  directions  and  give  no  ideas 
as  to  maxima  or  minima  in  the  curve  of  favorable 
conditions.  As  an  example,  consider  the  equilibrium 


Pent  Pmo 

where  K  equals  approximately  o.ooi  for  500°  C.;  at 
900°  C.  the  equilibrium  constant  for  the  same  re- 
lationship has  the  approximate  value  K'  346,  or  346,000 
times  as  great.  This  illustrates  the  importance  of 
getting  numerical  values  for  the  constants  expressing 
equilibrium  conditions  for  the  various  gases,  even 
though  they  be  approximate. 

From  a  consideration  of  the  CO,  H2,  CH4,  and  H2O 
equilibrium,  it  appears  that  excesses  of  H2  and  CO 
would  be  favorable  to  the  formation  or  preservation  of 
hydrocarbons  both  at  500°  C.  and  900°  C.  It  will 
further  appear,  however,  that  at  900°  C.  the  excess  of 
H2  and  CO  to  stimulate  the  reaction  towards  hydro- 
carbons will  have  to  be  enormous,  while  at  500°  C. 

do) 


it  need  be  only  moderate.  This  can  be  seen  from  a 
mathematical  study  of  the  equilibrium,  purely 
aside  from  the  chemistry  involved.  At  500°  C.  the 
denominator  is  obviously  the  predominant  factor. 
At  900°  C.  the  numerator  has  become  the  predominant 
factor.  In  fact  the  situation  is  so  different  that  it 
would  take  many  times  as  much  H2  and  CO  at  900°  C. 
as  it  would  at  500°  C.  Taking  the  two  equilibrium 
constants  and  calculating  theoretical  mixtures  one 
obtains  the  following  contrasting  results: 

CH4  +  H2O  ^±  CO  +  3H2 

X  =  final  volume  CO  »/i  (1  —  4X)  =  final  volume  CH4 

3X  -  final  volume  H2  »/«  (1  —  4X)   =  final  volume  HZO 


K  = 


Temp. 
0  C. 


500. 
900. 


PCO     P3H2 

108  X* 

PCH4   0H20 

16  X'  —  8X  +  1 
Percentages 

0.001 

.      346 

CO           H2            CH4 

5               15              40 
24.3          72.9            1.4 

HiO 

40 
1.4 

The  water  vapor  of  these  equilibria  is  usually  not 
considered  in  practice  because  it  never  appears  in 
either  the  gas  of  the  tank  holder  or  in  the  gas  sampling 
tube  and  resulting  analysis.  This  does  not  prove  its 
absence  in  the  machine.  Also  equal  pressures  of  hy- 
drogen and  CO  in  a  given  system  are  not  necessarily 
of  the  same  influence.  This  is  shown  in  equilibrium 
conditions  for  the  CH4,  H20,  CO  and  H2  system, 
where  for  instance  the  concentration  of  H2  is  raised 
to  the  third  power,  while  that  of  CO  is  of  the  first 
power.  In  manufacturing  practice  the  total  pressure  is 
approximately  one  atmosphere,  the  partial  pressures 
are  expressed  by  such  decimals  as  0.5.  The  third  power 
of  0.5,  or  0.125,  is  much  less  than  the  first  power,  0.5. 
Examples  to  show  the  effect  of  temperature  crn  the 
state  of  equilibrium  can  be  found  in  straight  hydro- 
carbon reactions.  The  equilibrium  between  acetylene 
and  benzene  shows  the  following  results: 

600°  C  900°  C  2000°  C 

K  =  ,^'J?'  9  X  io23  1.2  X  io13         6  X  io-4 

((^ztizr 

It  appears  that  the  value  of  K'  at  2000°  C.  is  1.5  X 
io27  times  as  great  as  the  value  of  K  at  600°  C.  This 
leads  to  the  expectation  that  while  at  600°  C. 
all  the  acetylene  tends  to  polymerize  to  benzene, 

(n) 


at  2000°  C.,  under  proper  conditions  of  pressure, 
benzene  tends  to  depolymerize  to  acetylene. 

In  the  equilibrium  existing  between  ethane  and 
ethylene, 

C2H6  =  C2H4  +  H2  —  37900  cal., 

the  value  of  K'  at  900°  is  approximately  1.28,  whereasthe 
value  of  K  at  150°  is  approximately  0.00000000000007. 
Ethane  at  900°  C.  has  a  pronounced  tendency 
to  go  to  ethylene;  the  tendency  for  the  ethylene  to 
combine  with  hydrogen  at  150°  C.  to  form  ethane  is 
even  more  pronounced.  The  relatively  small  amount 
of  ethane  in  oil  gas  made  at  900°  C.  would  seem  to 
verify  the  first  equilibrium  constant;  the  large  yield 
of  ethane  through  the  reduction  of  ethylene  with 
hydrogen  in  the  presence  of  palladium  at  150°  C.  in- 
dicates the  second  constant. 

EFFECT    OF   PRESSURE    ON    GASEOUS    REACTIONS 

In  passing  from  ethane  to  acetylene,  C2H6  =  C2H2  + 
2H2,  there  is  an  increase  in  volume;  on  the  other  hand, 
when  acetylene  polymerizes  to  benzene,  3C2H2  — > 
C6H6,  there  is  a  decrease  in  volume.  According  to 
the  principle  of  LeChatelier  one  would  not  expect 
the  same  pressure  conditions  to  be  favorable  to  both. 
Again,  the  information  is  qualitative  and  gives  no 
concrete  idea  of  the  relative  influence  of  one-third 
atmosphere  when  added  to  one  atmosphere  pressure 
absolute  as  compared  to  adding  the  same  one-third 
atmosphere  to  ten  atmospheres  pressure  absolute.  As 
a  type  reaction  consider 

B2 

A  — >•  26  where  K  =  - 
A 

For  numerical  illustration,  assume  the  value  of  K  to 
be  equal  to  i  (any  other  value  serving  equally  well). 
From  this,  one  finds  for  partial  pressures, 
when  A  =  100,  B  =  10  or  when  A  =  o.oi,  B  =  o.i. 
In  the  first  case  the  partial  pressure  of  A  is  ten  times 
as  great  as  that  of  B;  in  the  second  case  the  partial 
pressure  of  A  is  only  one-tenth  as  large  as  the 
partial  pressure  of  B.  In  other  words,  by  simply 
changing  the  total  pressure  on  the  system  and  keeping 
all  other  conditions  constant,  the  ratio  of  A  to  B  for 
the  pressures  shown  has  been  divided  by  100.  By 
taking  the  first  differential  of  the  relationship,  and 
equating  it  to  o, 

B2  B2  dA        26 

K  =  —         A=  —  =  —  =  o  ,B=o 

A  K  dE          K 

(12) 


one  sees  there  is  a  maximum  or  minimum  in  the  ratio 
of  A  to  B  as  zero  pressure  is  approached.  By  taking 
the  second  differential 


"      h 


K 

one  finds  the  sign  to  be  positive,  indicating  that  the 
partial  pressure  of  A  as  compared  with  the  partial 
pressure  of  B  approaches  a  minimum  as  the  pressure 
approaches  the  absolute  zero;  or  conversely  there 
would  be  a  maximum  relative  yield  of  B  the  closer 
one  approached  zero  pressure  absolute.  The  rate  of 
change  can  best  be  seen  by  determining  points  for  the 
parabola,  B2  =  KA,  and  plotting  the  resulting  curve.1 


0%A,100%B 


1007.A.07.B 

™     .l^tJ      .3  1       '•"* 

Total  Pressure  in  Atmospheres 

FIG.  I — REACTION  ISOTHERM 

The  general  relationship  of  B  to  A  changes  only  in 
degree  the  greater  the  change  in  the  number  of  volumes, 
as  can  be  seen  by  considering  the  curve  for 


A-3B, 


0%A,100%B 


100%A,0%B0J 

0  J44    S 


Total  Pressure  in  Atmospheres 


FIG.  II — REACTION  ISOTHERM 

1  Since  most  of  the  values  of  K  encountered  in  the  practical  study  of 
the  problem  were  represented  by  decimals,  Curves  I  and  II  were  plotted 
on  the  basis  of  K  ==  0.1. 

(13) 


From  the  curves  shown,  one  can  readily  see  that  the 
effect  of  reducing  pressure  from  one  atmosphere  to 
two-thirds  of  an  atmosphere  gives  an  advantage  which 
is  of  little  practical  consequence  when  compared  with 
the  advantage  gained  by  the  same  reductions  when 
nearer  the  absolute  zero  of  pressure.  One-thirtieth  of 
an  atmosphere  added  to  one-thirtieth  atmosphere  pres- 
sure doubles  the  total  pressure  on  a  system  just  as 
effectually  as  an  increase  from  100  to  200  atmospheres. 

EFFECT  OF  CONCENTRATION  IN  GASEOUS  REACTIONS 

The  addition  of  an  end  product  in  any  decomposition 
or  dissociation  process,  such  as 

PCls  >  PCla  +  Clj 

NH4C1  >  NH3  +  HC1 

2SO3  >  2SO2  +  O2 

2NH3  >•       N2  +  3H2 

checks  the  decomposition  or  dissociation.  In  other 
words,  less  PC15  will  dissociate  in  an  atmosphere  of 
chlorine  than  in  an  atmosphere  of  nitrogen  or  air. 
Ammonium  chloride  when  heated  in  an  atmosphere  of 
ammonia  will  not  dissociate  to  the  same  extent  as  in  a 
vacuum  or  in  an  atmosphere  containing  neither 
arhmonia  nor  hydrochloric  acid  gas.  Likewise  it  would 
be  expected  that  ethylene  would  not  decompose  to  the 
same  degree  when  subjected  to  a  high  temperature  in 
the  presence  of  hydrogen  as  when  subjected  to  the 
same  temperature  in  an  atmosphere  of  nitrogen. 
Further,  if  the  ethylene  were  subjected  to  the  same 
high  temperature  in  the  presence  of  both  hydrogen 
and  methane,  these  two  constituents  in  the  ethylene- 
methane-hydrogen  equilibrium  could  be  in  excess; 
as  a  result,  less  of  the  ethylene  should  be  decomposed 
in  the  formation  of  methane  and  hydrogen.  In  the 
same  way  if  petroleum  is  cracked  in  an  atmosphere  con- 
taining all  the  hydrocarbon  gases  with  the  exception 
of  ethylene,  one  would  expect  all  the  fixed  gas  coming 
from  the  petroleum  to  be  ethylene,  at  least  until  the 
ethylene  content  of  the  system  is  sufficient  to  conform 
to  the  equilibrium  conditions.  The  consideration  of 
these  principles  seems  to  question  the  necessity  of  using 
valuable  gas  oil  in  continually  generating  new  end 
products,  such  as  tar  and  hydrogen;  if  they  could  be 
artificially  supplied  the  equilibrium  conditions  would 
be  satisfied  without  producing  new  decomposition  and 
polymerization  end  products. 

COMBINED    INFLUENCE    OF    PRESSURE    AND    CONCENTRA- 
TION   ON    GASEOUS    REACTIONS 

Theoretical   consideration   of  the   effect   of  pressure 

(14) 


on  gaseous  reactions  indicates  that  an  increased  yield 
of  gaseous  hydrocarbons  will  be  obtained  as  the  total 
pressure  on  the  system  approaches  zero;  also  an  in- 
creased yield  of  illuminants  will  be  obtained  by  crack- 
ing the  oil  in  an  atmosphere  of  end  products  such  as 
hydrogen  and  methane.  On  combination  the  logical 
conclusion  is  that  one  should  obtain  the  maximum 
yield  of  illuminants  by  cracking  the  petroleum  at  low 
pressures  and  in  an  atmosphere  of  end  products. 
Upon  first  consideration  one  might  reasonably  ques- 
tion the  idea  of  adding  hydrogen  or  methane  to  a 
vacuum,  but  this  investigation  deals  with  relative 
partial  pressures,  regardless  of  whether  the  total 
pressure  equals  fifty  atmospheres  or  one-fiftieth  of  one 
atmosphere  absolute. 

INFLUENCE    OF    CATALYSTS    ON    GASEOUS    REACTIONS 

Catalytic  agents  such  as  platinum,  palladium, 
cobalt  and  nickel  do  not,  in  any  way,  influence  final 
conditions  of  equilibrium;  they  merely  hasten  the  rate 
at  which  the  system  reaches  its  final  equilibrium. 
Whereas  ethylene  and  hydrogen  do  not  combine  to  an 
appreciable  degree  when  heated  to  100°  C.  in  the 
absence  of  a  catalyzer,  the  same  mixture  passed  over 
colloidal  palladium  heated  to  100°  C.  unites  to  form  a 
considerable  percentage  of  ethane.  Likewise  CO  and 
H2  or  CO2  and  H2  can  be  in  intimate  contact  at  200° 
to  300°  without  appreciable  reaction  in  the  formation 
of  methane,  but  when  the  same  proportions  are  brought 
together  in  the  presence  of  a  catalytic  agent  such  as 
nickel  or  cobalt  there  is  a  very  large  yield  of  methane 
and  water.1  Vignon2  finds  that  lime  has  much  the  same 
effect  on  the  combination  of  CO  and  H2. 

THE    VAN'T    HOFF    DIFFERENTIAL    EQUATION    SHOWING 

THE    RELATION    OF   K    TO    K' 

To  all  students  of  physical  chemistry  the  proposi- 
tion of  Berthelot  and  Thomson  that  "every  chemical 
change  gives  rise  to  the  production  of  those  substances 
which  occasion  the  greatest  development  of  heat" 
is  familiar.  Were  this  true,  it  would  be  easy  to  pre- 
dict which  of  two  given  reactions  would  take  place 
at  a  given  temperature.  Chemists  today  recognize 

1  Mayer,    Henseling   and  Altmayer,    Jour.  f.  Gasb.,  1909,  pp.  166,  194; 
Jockutn,  Ibid.,  1914,  pp.  73,  103,  124,  149;  Orlow,  Jour.  Russ.  Phys.  Chem., 
1908,  p.  1588. 

2  Vignon.  I,.,  Compt.  rend.,  1913,  pp.  131-134. 

(15) 


the  fallacy  of  the  statement  because  in  all  chemical 
reactions  one  deals  with  the  additional  so-called 
"  latent  energy."  Berthelot's  principle  disregards  this 
molecular  energy,  and  assumes  the  free  energy,  termed 
maximum  work,  to  be  equal  to  the  total  energy  change. 
Nernst  maintains  that  this  is  true  only  at  the  absolute 
zero,  i.  e.,  the  entropy  of  liquids  and  solids  at  absolute 
zero  temperature  equals  zero. 

The  van't   Hoff  equation  showing  the  relation  be- 
tween K  and  K'  is  expressed  by 


(log,  *,)  =  or     d  (log,  *,)  = 

Upon  integration  this  becomes 

log,  **  =  RT  +  constant 

Were  it  a  simple  matter  to  determine  the  value  of 
this  constant  of  integration,  as  well  as  the  value  of 
q  at  the  different  temperatures  (in  other  words  integrate 
the  expression  to  absolute  units)  this  would  consti- 
tute a  mathematical  expression  for  what  many  consider 
a  third  law  of  thermodynamics.  As  yet  there  is  no 
such  accepted  integration,  and  the  best  solution  is 
to  use  approximate  expressions,  remembering  at  all 
times  that  the  expressions  are  approximate,  and  making 
intelligent  use  of  them  as  such.  It  is  possible  to 
avoid  the  constant  of  integration,  however,  by  inte- 
grating between  limits  p'  and  p  to 

log,  Kp>  —  log,  Kp  =  9~    (~  —  ^) 

This  integrated  expression  is  extremely  important 
in  determining  the  value  of  K'  for  any  desired  tempera- 
ture after  the  value  of  K  for  any  other  temperature 
has  been  experimentally  determined.  It  is  also  valu- 
able in  showing  relationships  between  K  and  K' 
for  two  different  temperatures,  where  neither  has 
been  determined,  but  in  this  case  it  expresses  relation- 
ships and  not  direct  values.  For  instance,  assume 
that  one  wished  to  find  the  relationship  between  K 
and  K'  for  the  reaction 

2C  +  H2  =  C2H2  —  58100  cal. 
at  the  temperatures  600°  and  900°  C. 


log,  *,,  -  log,  Kt  -  -  -  =  8.49 

(16) 


loge  KP    =  8.49    or,  logio  ^~    =  3-69 

whence  Keoo  =  ~ 

4900 

THE  NERNST  APPROXIMATION  FORMULA  FOR  K 

Even  though  correct,  K  is  a  value  based  on  the  as- 
sumption that  sufficient  time  elapses  to  allow  the  sys- 
tem to  reach  complete  equilibrium.  When  dealing 
with  hydrocarbons  at  different  temperatures,  this 
must  not  be  overlooked.  In  fact  the  time  element 
is  of  such  primary  moment  that  numerically  correct 
values  for  K  would  be  of  little  more  practical  use  in 
gas  manufacture  than  approximate  values.  In  the 
case  of  reacting  gases  one  does  not  have  the  speed 
conditions  that  ordinarily  exist  in  solutions.  On 
the  other  hand,  gases  brought  together  at  sufficiently 
high  temperatures  do  reach  equilibrium  practically 
instantly.  It  is  important  to  bring  out  these  limita- 
tions despite  the  value  of  approximate  quantitative 
expressions  such  as  the  Nernst  formula;  the  latter  is 
of  immense  value  in  predicting  the  tendency  of  a  reac- 
tion. In  this  paper  Nernst 's  formula  is  merely  used; 
its  derivation  with  comments  can  be  found  in  the 
seventh  German  edition  of  Nernst 's  "  Theoretical 
Chemistry,"  Jellinek's  "  Physikalische  Chemie  der 
Gasreaktionen,"  or  Sackur's  "  Thermochemie  und 
Thermodynamik." 

log  K  =      -£-=  +  2v  1.75  log  T  +  ZvC 

4-571  -1 

where  q  is  the  heat  developed  at  ordinary  tempera- 
tures and  under  constant  pressure,  as  taken  from 
thermochemical  tables;  2z>  represents  the  volume 
changes,  and  2^C  represents  a  summation  of  constants. 
These  constants  are  given  as  follows: 

H2     1.6    C2H6  2.6    C2H2  3.2    CO  3.5    H2O   3.6 
CH4   2.5    C2H4  2.8    C6H6  3.0    COj  3.2    O2    2.8 

To  use   Nernst's  words,  the  equation  gives  a  "fairly 
accurate"  idea  of  the  state  of  equilibrium  in  a  system. 
The  approximation  is  applied  in  this  fashion: 
C  +  2H2  =  CH4  -f  18900  cal. 

+  18900 
log  Keoo  =  475yi        8?3    —  1.75  log  873    — 0.7  =  — 1 . 1 1   =  2.89(a) 

+  18900 
logKTso  -  — ?1  x  1Q23  —  1-75  log  1023  —  0.7   =  —1.93  =  2.07 

+  18900 
log  K»oo  =  457i~^77Y73~  1.75  log  1173  —  0.7   =  —2.55  =  3.45 

whence, 

Keoo  =  0.077  KTSO  -  0.012  K9oo  -  0.003 

(a)  Negative  logarithms  must  be  converted  into  logarithms  with  positive 

(17) 


In  similar  manner,  the  values  of  K,  K'  ',  and  K"  for 
Equations  i,  2,  3,  4,  5,  6,  7,  13,  16,  17,  18,  and 
22  in  Table  II  have  been  calculated.  In  those 
reactions  involving  CO  and  CO2,  as  19,  23,  and  26, 
use  has  been  made  of  the  approximation  formulas 
for  the  same  as  worked  out  by  Mayer  and  co-workers,1 
but  substituting  the  values  of  q  shown  in  the  table. 

CALCULATION    OF    HEATS    OF    REACTIONS    FOR    DIFFERENT 
EQUILIBRIA 

The  heat  absorbed  or  emitted  in  a  given  reaction 
was  determined  by  means  of  the  ordinary  thermochem- 
ical  methods  of  addition  and  subtraction,  as  in  the 
following  typical  examples: 

(a)     2C  +  8H  =  2CH«  +  37800  cal. 

2C  +  4H  =  CgH4  —  14600  cal. 

2CHU  =  C2H4  +  2H2  —  52400  cal. 
(6)     6C  +  6H  =  3C2H2  —  174300  cal. 

6C  +  6H  =     C«H»  —     11300  cal. 

3CZH2  =     C6H6  +  163000  cal. 
(c)      C  +  2H2  =  CH4  +  18900  cal. 

2H  +  O  =  HiO  +  58300  cal. 

CH4  +  H2O  =  3H2  +  C  +  O  —  77200  cal. 

C  +  O  =  CO  +  29000  cal.  _ 

CH4  +  H20  =  3H«  +  CO  —  48200  cal. 

It  is  likewise  possible  to  combine  the  values  of  K  for 
one  reaction  with  K'  for  a  second  reaction  in  order 
to  determine  K"  for  the  resultant  reaction. 

C  +  2H2  =  CH4         K  = 


P  Hi 

2C  +  H2  =  C2H2         K'  = 


Put 

Dividing  the   square   of  the   methane   equilibrium   by 
the  acetylene  equilibrium,  one  gets 


= 


This   operation   can   be   represented   by   the   equation 

2CH4  =  C2H2  +  3H2 

In  this  work  the  values  of  K  and  K'  have  been  com- 
bined in  the  manner  just  shown  in  order  to  determine 
values  for  equations  8,  9,  10,  n,  12,  14  and  15.  The 
Nernst  approximation  formula  could  be  applied  di- 
rectly to  each  of  these  equations  with  the  same  results. 
All  reactions  indicated  in  Table  II  may  go  in  either 
direction.  Attention  is  called  again  to  the  fact  that 
the  reactions  given  must  be  used  with  a  consideration 
of  all  factors  involved;  no  equation  by  itself  repre- 

1  Mayer,  Henseling  and  Altmayer.  Jour.Gasb.,  1909,  pp.  166,  194,  238. 
(18) 


sents  a  complete  system.  All  the  gases  mentioned, 
together  with  many  others,  are  tending  to  reach 
equilibrium  with  one  another.  Tar  compounds  were 
not  listed.  Benzene,  C6H6,  has  been  used  as  typical 
of  all  tar  formations.  In  technical  practice  one  gets 
benzene  and  other  tar  compounds  from  methane 
hydrocarbons;  from  experimental  evidence,  it  is 
known  that  from  ethylene1  or  acetylene2  the  same  re- 
sults are  reached.  Throughout  the  literature  one 
finds  questions  as  to  whether  methane  goes  to  acetylene, 
or  acetylene  to  methane,  ethane  to  ethylene,  ethylene 
to  ethane,  etc.  Considered  in  the  light  of  this  study 
it  appears  that  regardless  of  which  hydrocarbon  is 
used  initially  there  is  a  pronounced  tendency  for  the 
system  to  reach  a  common  equilibrium  dependent  upon 
the  existing  temperature.  With  hydrocarbons  the 
result  seems  to  depend  more  upon  conditions  of  temper- 
ature, pressure  and  concentration  than  upon  the  initial 
hydrocarbons.  In  other  words,  with  proper  condi- 
tions of  temperature,  pressure  and  concentration,  and 
with  sufficient  time  for  complete  reaction,  the  final 
equilibrium  will  be  that  of  the  mentioned  hydrocarbons 
and  their  reaction  products,  regardless  of  whether 
decane,  hexane,  ethane,  methane,  ethylene  or  acetylene, a 
singly  or  in  mixtures,  are  used  in  the  beginning. 

Table  II  furnishes  the  basis  for  the  experimental 
work  of  this  research.  Its  interpretation  serves  as 
a  guide  in  determining  the  direction  of  experiments.. 
Taking  Equation  9  as  typical,  where  K600  =  o.ooooooi 
and  Kgoo  =  0.0004,  it  seems  advisable  to  exceed 
900°  C.  in  temperature.  However,  referring  to 
KWO  =  0.077  and  K9QQ  =  0.003  f°r  Equation  3,  it  is 
evident  that  the  rate  at  which  methane  would  de- 
compose to  carbon  and  hydrogen,  in  accordance  with 
Equation  3,  easily  might  be  sufficient  to  offset  all 
C2H4  formation,  in  accordance  with  Equation  9. 

Considering  Equations  16  and  19,  two  of  the  most 
vital  in  present  carbureted  water  gas  manufacture,  one 
finds 

Ksoo  KTSO  Kso9 

16      C  +  H20  "^Z±.  CO  +  Hj 0.2  3.1  25.0 

19     rw.  +  w.n   ^        rr>  -i  STT«.       o.06        8.7        346.0 

1  Ipatiew,  Ber.,  1911,  p.  2978;  Ipatiewand  Rontala,  Ibid.,  1913,  p.  1748. 

2  R.  Meyer ./&»•<*.,  1912,  p.  1609;  Meyer  and  Tanzen,  Ibid.,  1913,  p.  3183. 
•  W.  A.  Bone.  Jour.  f.  Gasb.,    1908,    p.   803;    D.   T.    Day,    Am.    Chem. 

Jour.,  1886,  p.  153;  V.  Lewes,  Proc.  Roy.  Soc.,  1894,  p.  90;  Worstall 
and  Burwell,  Am.  Chem.  Jour.,  1897,  p.  815;  Bone  and  Coward,  Jour. 
Chem.  Soc.,  1908,  p.  1197;  Sabatier  and  Senderens,  Compt.  rend.,  130, 
1559;  C.  Paal,  Chem.  Ztg..  1912,  p.  60;  Ipatiew,  Ber.,  44,  2987. 

(19) 


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(20) 


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(21) 


and  that  a  temperature  of  900°  C.  is  favorable  to  the  CO1 
and  H2  formation  of  16,  but  unfavorable  to  the  methane 
preseryation  in  Equation  19.  On  the  other  hand, 
a  temperature  of  600°  C.  is  unfavorable  to  preserva- 
tion of  CO  and  H2in  Equation  16  but  is  more  favorable 
than  900°  to  hydrocarbon  formation  or  preservation. 
Also  it  is  more  favorable  to  formation  of  CO2  as  shown 
by  Equation  17.  These  temperature  effects  can  be 
more  clearly  understood  by  reference  to  the  first 
numerical  problem  cited,  and  to  the  theoretical  mix- 
tures given  for  Equation  19  at  temperatures  of  600 a 
and  900°  C.  It  appears  impossible  to  find  a  tempera- 
ture favorable  to  both  when  the  two  reactions  are 
simultaneously  carried  out.  In  order  to  preserve 
the  hydrocarbons  it  becomes  necessary  to  form  H2O, 
C02  and  deposit  carbon;  or  in  order  to  avoid  forming 
water  vapor,  C02  and  deposit  carbon,  it  becomes 
necessary  to  destroy  hydrocarbons.  The  two  cannot 
be  reconciled. 

SUMMARY 

On  theoretical  grounds,  therefore,  it  appears: 

I — Possible  to  create  such  conditions  that  the  oil 
cracking  process  can  be  carried  out  at  a  higher  tempera- 
ture than  is  now  used  in  oil  gas  processes,  and  thereby 
greatly  increase  the  yield  of  valuable  hydrocarbons. 

II — Possible  to  "crack"  oil  without  depositing  carbon, 
and  without  the  formation  of  water  vapor  and  CO2. 

Ill — Possible  to  partially  control  the  quantity  and 
composition  of  "tar"  produced  in  gas  manufacture. 

IV — Impossible  to  preserve  hydrocarbons  and  at 
the  same  time  avoid  CO2,  water  vapor,  and  deposited 
carbon,  when  oil  is  "cracked"  as  in  the  present  car- 
bureted water  gas  process. 


(22) 


THERMAL  REACTIONS  IN  CARBURETING  WATER  GAS 


PART  II— EXPERIMENTAL 

In  the  design  of  an  experimental  apparatus  for 
cracking  oil  in  accordance  with  the  theory  set  forth 
in  Part  I,  it  is  necessary  to  provide  accurate  control 
over  the  three  variables:  temperature,  pressure,  and 
concentration.  The  plan  of  research  has  been:  (i) 
To  keep  pressure  and  concentration  constant  un- 
til the  effect  of  changing  temperature  is  understood; 
(2)  to  keep  the  temperature  constant  and  change  the 
total  pressure  on  the  system;  (3)  to  hold  both  tem- 
perature and  pressure  constant  and  crack  the  oil 
in  the  presence  of  other  gases  in  order  to  vary  the  con- 
centrations. 

Considerable  time  was  spent  in  designing  and  build- 
ing an  apparatus  which  would  be  stable,  durable, 
easy  of  access  and  replaceable  in  all  its  parts,  as  well 
as  under  complete  control  with  respect  to  tempera- 
ture, pressure  and  concentration.  The  machine  was 
further  designed  to  be  of  such  dimensions  and  capacity 
as  would  indicate  results  which  might  be  expected 
in  the  commercial  application  of  the  principles  in- 
volved. In  its  completed  form  the  apparatus  covers 
a  floor  space  sixteen  feet  by  four  feet  and  the  oil  feed 
cup  at  the  top  of  the  machine  is  nine  feet  from  the 
floor.  With  this  equipment  it  is  possible  to  main- 
tain any  temperature  up  to  1000°  C.  within  five  de- 
grees, and  any  pressure  ranging  from  one-thirtieth 
of  one  atmosphere  absolute  to  three  atmospheres 
absolute. 

FURNACE    BODY 

The  furnace  body  is  made  from  il/z  in.  "Reading" 
brand  wrought  iron  pipe,  32  in.  long.  For  a  length 
of  1 8  in.  the  pipe  is  wrapped  with  No.  15  Nichrome 
resistance  wire,  seven  turns  to  the  inch.  Between  the 
wrought  iron  pipe  and  resistance  wire  five  layers  of 
asbestos  paper  serve  as  insulation.  In  series  with  the 
nichrome  wire  of  the  furnace  is  a  large  rheostat,  with 
graduated  steps  between  2l/2  and  9  amperes.  An 
incandescent  tell-tale  lamp  is  connected  across  the 
binding  posts  of  the  furnace,  to  indicate  when  the 
current  is  on  as  well  as  to  give  a  rough  idea  of  the 

(23) 


(24) 


wattage  in  use.  Both  voltmeter  and  ammeter  are  con- 
nected in  the  circuit.  (See  Fig.  III.) 

The  nichrome  wire  windings  are  enclosed  in  a  five- 
inch  insulation  of  magnesia-asbestos  pipe  covering 
to  minimize  radiation.  A  3/4  in.  wrought  iron  pipe  is 
welded  at  right  angles  into  the  i1/^  in.  wrought  iron 
furnace  body  to  serve  as  a  container  for  the  pyrometer 
point.  This  side  tube  is  likewise  insulated  with  as- 
bestos and  is  fitted  with  a  stuffing  box  surrounding  the 
pyrometer  rod.  With  this  side  tube  it  is  possible 
to  keep  the  pyrometer  point  directly  in  the  furnace 
body  at  all  times.  The  pyrometer  couple  is  of  the 
iron-nickel  type  connected  with  a  millivoltmeter  cali- 
brated in  degrees  Centigrade. 

After  continued  use  at  the  higher  temperatures 
the  furnace  body  warps  or  the  nichrome  wire  burns 
out.  Duplicates  for  all  parts  are  kept  on  hand,  and 
the  apparatus  is  so  designed  that  any  part  may  be  re- 
placed within  a  few  minutes. 

In  order  to  vaporize  the  oil  before  it  reaches  the 
cracking  zone,  the  upper  part  of  the  furnace  tube  is 
filled  with  5/8  in.  steel  balls.  These  are  held  in  place 
by  a  thin  post  which  runs  vertically  through  the  fur- 
nace supporting  a  perforated  plate.  The  vertical  rod 
is  bent  to  permit  the  centering  required  for  the  pyrom- 
eter. The  object  of  the  steel  balls  is  to  spread  the 
oil  in  thin  films  and  facilitate  vaporization,  but  not 
to  serve  as  cracking  surface;  in  order  to  accomplish 
this  they  are  kept  at  a  safe  height  above  the  cracking 
zone.  .  Lowering  them  into  the  cracking  zone  has  a 
marked  influence  on  the  products  obtained  from  the 
cracking  process.  The  furnace,  together  with  con- 
denser, oil  feed,  pressure  gauge  and  admixture  gas- 
inlet  pipe  are  vertically  supported  by  iron  clamps  at- 
tached to  an  upright  3  in.  X  6  in.  yellow  pine  timber. 
The  assembled  apparatus  was  tested  at  100  Ibs.  hy- 
draulic pressure. 

OIL    FEED 

A  Powell  sight  feed  oil  cup  of  one  quart  capacity 
is  joined  by  a  3/4  in.  elbow  and  nipple  to  a  iVa  X 
iVa  X  3A  X  3A  in.  cross  which  forms  the  upper  end 
of  the  furnace  body.  The  pressure  in  the  oil  cup  is 
equalized  through  a  small  internal  pipe  which  communi- 
cates with  the  furnace  body  below  the  point  of  oil 
discharge.  As  a  result  of  this  equalizing  tube,  regard- 
less of  whether  the  apparatus  is  under  increased  or 
reduced  pressure,  the  oil  supply  is  always  under  a 

(25) 


supply  pressure  equal  to  its  own  head.  As  this  head 
decreases  the  rate  of  flow  may  be  regulated  by  the 
needle  valve  controlling  the  feed  inlet.  The  rate  of 
supply  may  be  determined  by  counting  the  drops  for  a 
given  time. 

PRESSURE    GAUGES 

For  all  vacuum  work  the  apparatus  is  connected  with 
a  mercury  manometer  calibrated  in  inches.  A  me- 
chanical vacuum  gauge  is  also  placed  at  the  top  of  the 
apparatus  to  indicate  a  free  path  in  the  cracking  tube. 
In  the  course  of  the  experiments  under  certain  condi- 
tions, sufficient  carbon  was  deposited  to  clog  up  the 
apparatus  and  show  a  considerable  difference  in  the 
pressure  between  the  two  gauges.  Such  a  condition, 
however,  is  limited  to  experiments  involving  high  tem- 
peratures and  pressures  (atmospheric  or  greater), 
where  the  deposition  of  carbon  is  at  its  maximum. 
There  is  never  any  clogging  under  reduced  pressures. 
For  pressure  work,  the  mercury  column  is  disconnected 
and  a  mechanical  pressure  gauge  is  substituted. 

CONDENSER 

At  the  lower  end,  the  generating  tube  or  furnace 
body  discharges  through  a  Liebig  type  condenser 
into  a  tar  drip  for  the  collection  of  liquid  condensates. 
The  cooling  water  enters  at  the  bottom  of  the  con- 
denser and  on  leaving  continues  through  the  jacket 
of  the  vacuum  pump.  The  condenser  pipe  is  off- 
set from  the  furnace  body  rather  than  placed  di- 
rectly under  it  so  that  the  furnace  may  be  cleaned 
by  simply  removing  the  lower  plug  and  withdrawing 
the  contents.  It  is  thus  possible  to  remove  and 
weigh  the  deposited  carbon  from  the  furnace  body 
after  each  run. 

TAR    DRIPS 

For  vacuum  work  the  tar  drips  are  of  glass,  as  this 
facilitates  observation  of  the  gas,  as  well  as  the  nature 
and  the  rate  of  tar  formation.  In  vacuum  work  it 
was  soon  found  that  the  lighter  condensates  would  con- 
tinue through  the  vacuum  pump  because  of  the  low 
pressure  in  the  first  tar  drip.  To  collect  the  liquids 
drawn  through,  a  second  tar  drip  was  placed  beyond 
the  vacuum  pump.  Upon  reaching  the  second  drip 
these  lighter  hydrocarbons  condense,  as  the  pressure 
is  then  approximately  atmospheric.  When  working 
under  one-thirtieth  of  an  atmosphere  it  was  found  that 
only  a  small  percentage  of  the  hydrocarbons  would 

(26) 


collect  in  the  first  tar  drip.      For  pressure  work  a  steel 
tar  collector  was  substituted. 

VACUUM    PUMP 

Vacuum  in  the  system  is  maintained  by  a  May- 
Nelson  two-ring  vacuum  pump.  By  means  of  a  by- 
pass connection  joining  the  outlet  and  inlet  of  the 
pump,  it  is  possible  so  to  regulate  the  valve  as  to  main- 
tain any  desired  vacuum  down  to  one-thirtieth  of  an 
atmosphere. 

CONNECTION    FOR    PRESSURE     WORK 

The  vacuum  pump  is  mounted  on  a  movable  con- 
crete foundation  and  by  disconnecting  a  few  couplings 
the  vacuum  attachments  may  be  removed.  For 
pressure  work  there  is  substituted  an  all  metal  tar 
collector,  connecting  pipe,  and  release  pressure  valve, 
as  shown  in  Fig.  IV.  The  apparatus  may  be  changed 
from  vacuum  to  pressure,  or  vice  versa,  in  twenty 
minutes.  When  working  under  pressure,  the  gas 

CUT  SHOWING 

PRESSURE  CONNECTIONS 

[IT 


FIG.   IV 

generated  in  the  furnace  body  creates  its  own  pres- 
sure. This  pressure  is  controlled  by  an  ordinary 
release  valve  placed  at  the  inlet  to  the  gas  collec- 
tor. By  regulating  the  release  of  this  valve,  the 
apparatus  may  be  set  to  work  under  any  pressure 
from  atmospheric  to  30  Ibs.  per  square  inch  above 
atmospheric,  which  seemed  to  be  the  upper  safe  work- 
ing limit  of  the  furnace  under  the  conditions  of  opera- 
tion. A  pressure  gauge  is  placed  in  the  discharge  line 
and  used  as  a  check  on  the  pressure  gauge  near  the  oil 
feed. 

GAS   COLLECTOR   AND   ADMIXTURE    GAS   TANKS 

The  gas  generated  is  collected  in  a  12  cu.  ft.  capacity 
gas  holder,  made  by  the  American  Meter  Company. 
The  tank  is  graduated  in  tenths  of  a  cubic  foot.  By 
multiplying  the  number  of  cubic  feet  by  28.32  the 

(27) 


volume  is  reported  in  liters.  To  avoid  relying  upon 
natural  diffusion  for  mixing  the  gases,  the  bell  of  the 
holder  is  fitted  with  an  internal  mechanical  stirrer 
directly  connected  through  a  stuffing  box  to  an  elec- 
tric motor  located  on  top  of  the  bell.  Perfect  mixing 
of  the  gases  may  be  attained  in  two  minutes  with  this 
equipment  whereas  natural  diffusion  would  require 
from  one  to  two  hours. 

The  equipment  also  contains  two  6  cu.  ft.  capacity 
admixture  tanks  of  the  same  design  as  the  large  holder. 
These  serve  as  gas  supply  tanks  when  cracking  oil  in 
the  presence  of  other  gases  such  as  H2,  CO,  or  mix- 
tures of  the  two.  A  l/4  in.  steel  pipe,  fitted  with 
needle  control  valves,  connects  these  two  tanks  with 
the  inlet  end  of  the  furnace  body.  The  piping  is  so 
arranged  as  to  connect  any  two  of  the  three  tanks. 

METHOD    OF    MAKING    A    RUN 

When  the  apparatus  is  operated  under  vacuum  the 
furnace  body  is  first  heated  by  the  resistance  coils 
to  the  desired  temperature  for  cracking  the  oil  into 
fixed  gases.  The  oil  is  permitted  to  enter  the  upper 
part  of  the  generating  tube  where  it  spreads  over  the 
steel  balls  and  is  vaporized.  In  the  meantime,  the 
vacuum  pump  has  been  set  in  operation  and  draws 
the  oil  vapors  downward  into  the  cracking  zone  of 
the  furnace  body,  whereupon  these  vapors  are  imme- 
diately cracked  into  fixed  gases  and  other  products. 
These  products,  before  opportunity  is  offered  for 
polymerization  or  decomposition  of  the  hydrocarbon 
gases,  are  withdrawn  by  the  vacuum  pump  from  the 
cracking  zone  and  their  place  is  taken  by  a  quantity 
of  oil  vapor  from  the  vaporizing  zone  above.  In 
this  manner  the  hydrocarbon  gases  are  withdrawn 
continuously  and  as  quickly  as  they  form.  After 
they  pass  through  the  condenser  and  receiver  for  the 
removal  of  the  condensable  vapors,  they  are  for- 
warded by  way  of  the  pump  to  the  gas  holder. 

GAS    SAMPLING    AND    ANALYSIS 

After  the  gas  in  the  holder  is  thoroughly  mixed 
by  the  mechanical  stirrer,  three  or  four  sampling 
tubes  are  filled  for  analysis.  As  a  guide  for  all  meth- 
ods of  gas  analysis,  Dennis'  1913  edition  of  "Gas 
Analysis,"  using  the  Hempel  equipment,  is  followed. 
To  determine  the  hydrogen  in  a  mixture  of  hydrogen, 
methane  and  ethane,  Hempel's  fractional  combus- 
ts) 


tion  method1  is  used.     All  analyses  are  made  in  dupli- 
cate. 

DATA    OBTAINED    FROM    A    RUN 

In  this  work  all  conditions  outside  of  temperature, 
pressure,  and  concentration  were  maintained  as  uni- 
form as  possible.  Four  hundred  cc.  of  oil  were  used 
per  run,  fed  at  the  rate  of  about  3  cc.  per  minute. 
The  oil  used  is  technically  known  as  "150°  (F)  water 
white  oil;"  its  specific  gravity  at  15°  C.  is  0.7984; 
boiling  point  between  150°  and  290°  C.  Oil  from 
the  same  tank  was  used  throughout  the  experiments. 
All  runs  were  made  in  duplicate. 

TABLE  I — TYPICAL  VACUUM  RUN  RECORD 

Oil  used,  400  cc.  Room  temperature,  15°  C.  Barometer,  756  mm. 

Oil  feed 

Drops  in    Cu.  ft.  gas 
10  sec.     observed 

24  

26  2.16 

23  3.01 
21  3.76 

24  *  4.86 
26        6.86 

25  7.76 
17        8.36 

8.75 

Corrected  to  standard  conditions  as  follows: 

8.75  X  ^  X  ^  X  28.32  =  234  liters 

ANALYSIS  OF  PRODUCTS  FROM  TABLE  I — GAS  ANALYSIS 

Per  cent  L/iters  at 

by  vol.  std.  cond. 

C02 0.1 

111 52.1  122.0 

O2 0.9  

CO 0.4  

CH4 24.0  56.0 

C2H6 1.3  3.0 

H2 17.3  40.0 

N2  (difference) 3.9 


Temp. 

Vacuum 

Time 

C. 

Inches 

11.43 

900 

29.00 

12.00 

903 

28.50 

12.15 

905 

28.00 

12.30 

895 

28.75 

12.45 

895 

28.75 

1.00 

895 

28.50 

1.30 

895 

28.50 

1.45 

895 

28.50 

2.00 

895 

28.75 

2.07 

Run  ended 

100.0  

Carbon,  3  grams. 

"Tar"   60  cc.     Sp.   gr.   20°   Be. 

EFFECT    OF    TEMPERATURE    CHANGES 

The  experimental  data,  on  changes  in  temperature 
in  the  cracking  of  the  oil,  with  pressure  and  concen- 
tration maintained  constant,  agree  with  the  data  re- 
corded in  the  literature  from  the  experiments  by  Haber,2 

1  Zeitsch.  angew.  Chem.,  1912,   1841. 

2  Journal  f.  Cash.,  1896,  799,  813,  830. 

(29) 


Hempel,1  Ross  and  Leather,2  Lewes,3  Fulweiler,4 
and  others.  It  is  difficult  to  make  accurate  compari- 
sons of  two  experiments  conducted  in  different  appa- 
ratus on  account  of  the  great  variety  of  conditions 
involved.  Subjecting  a  gas  to  a  temperature  of  900° 
C.  for  five  seconds  is  quite  different  from  subjecting  it 
to  the  same  temperature  for  five  minutes.5  Leading 
the  gases  through  a  l/s  in.  pipe  heated  to  900°  C. 
would  give  different  results  from  those  obtained  by 
leading  the  same  gases  through  a  2  in.  pipe  heated  to 
900°  C.  While  the  difference  due  to  experimental 
apparatus  would  not  be  so  great- as  the  examples  cited, 
there  is  sufficient  difference  to  affect  the  value  of  direct 
comparison. 

However,  the  general  results  obtained  at  different 
temperatures  by  different  experimenters  are  compara- 
ble. As  the  temperature  increases,  the  quantity  of 
valuable  gas  from  a  given  amount  of  oil  increases  to 
a  maximum,  after  which  the  gaseous  hydrocarbons 
rapidly  decrease  and  the  deposited  carbon  increases. 
The  quantity  of  tar  decreases,  but  this  is  due  to  a  dis- 
sociation of  the  hydrocarbons  and  cannot  be  construed 
favorably.  Upon  subjecting  the  oil  to  temperatures 
of  650°,  750°  and  900°  C.,  under  atmospheric  pressure, 
the  results  are  as  follows: 


Tar 
Cc. 

163 
80 
11 


TABLE  II 

Oil  used,  400  cc. 

Temp. 
0  C. 

Press. 

Gas  liters 
Standard 
conditions 

Carbon 
Grams 

650 
750 
900 

atmos. 
atmos. 
atmos. 

135 
206 
382 

3 
18 
115 

Analysis  of  Gas  from  Table  II 


Temp. 

C2H6 

CH4 

H2 

111 

0  C. 

Per  cent 

Per  cent 

Per  cent 

Per  cent 

650 

10.2 

33.7 

9.1 

43.6 

750 

4.9 

41.1 

19.2 

30.6 

900 

None 

46.7 

38.6 

13.1 

EFFECT     OF     INCREASED     PRESSURE     ON     GASEOUS     REAC- 
TIONS 

It  seems  reasonable  to  expect  that  a  high  pressure 
will  assist  materially  in  condensing  three  volumes  of 
acetylene  into  one  volume  of  benzene:  3C2H2  <  >  CeH6. 

'  Journal  f.  Gasb.,  1910,  53. 

2  Journal  of  Gas  Lighting,  1906,  825. 

3  Jour.  Soc.  Chem.  Ind.,  1892,  584. 

4  Rogers'  "industrial  Chemistry." 

*  Lewes,  Proceedings  of   Royal    Soc.,   1894,   90;  W.  A.   Bone,  Jour.  f. 
Gasb.,  1908,  803;  Bone  and  Coward,  Jour.  Chem.  Soc.,  1908,  1 197. 

(30) 


2001 


.£ 

I  too 


i" 


HXH 

80 
60 
40 
20 


10 


Gas 


10  20    PrM$ure30 


Carbon 


20 


30 


40      Pres. 


Tar 


10  20 


30 


40     Pres 


CH4 


10  20  30 

750°C. 


40     Pres 


FIG.  V— VARIATIONS  IN  YIELDS  OP  PRODUCTS  AT  750°  C.,  UNDER  VARYING 
PRESSURES.     (TABLES  II,  III,  IV  AND  VI) 

(31) 


40 
20 


III. 


10  20  30  40         Prcs. 


III. 


10  20  30  40         Prts 


20  30  40 


C2H6 


10  20  30  40         Pre 


750°  C. 


vi— VARIATIONS  IN  YIELDS  OP  PRODUCTS  AT  750°  C.,  UNDER  VARYING 
PRESSURES.     (TABLES  II,  III.  IV  AND  VI) 

(32) 


On  the  other  hand,  it  seems  reasonable  to  expect  that, 
under  a  high  pressure,  it  will  be  considerably  more 
difficult  for  one  volume  of  oil  vapor  to  break  up  or 
expand  to  many  volumes  of  gas  than  under  reduced 
pressure. 

In  the  system 

OIL         T^         GAS         "^1         TAR 

(Few  volumes)  (Many  volumes)  (Few  volumes) 

one  would  expect  that  the  application  of  high  pres- 
sures would  increase  the  difficulty  of  generating  gas, 
and  after  the  gas  is  generated  it  would  make  easier 
the  condensation  reactions  which  proceed  to  the  tar 
stage.  Since  the  unsaturated  hydrocarbons,  ethylene 
and  acetylene,  polymerize  most  readily,  increased 
pressure  should  preferably  condense  them  with  the 
formation  of  tar  compounds.  In  addition  to  the  direct 
influence  of  pressure,  it  may  be  assumed  that  when 
working  under  increased  pressure  the  gaseous  hydro- 
carbons are  subjected  to  the  influence  of  heat  for  a 
longer  time,  which  further  tends  towards  the  forma- 
tion of  heavy  condensation  products  at  the  expense 
of  the  illuminants.  The  following  series  of  experi- 
mental results  appears  to  justify  these  conclusions: 


TABLE  III 

Oil  used,  400  cc. 

Pressure 

Temp. 

Absolute 

Gas 

Carbon 

Tar 

°C. 

Lbs. 

Liters 

Grams 

Cc. 

650 

45 

145 

8 

133 

750 

45 

194 

26 

87 

900 

45 

310 

165 

9 

Analysis  of  Gas  from  Table  III 


Temp. 

CtH6 

CH4 

H2 

111 

°C. 

Per  cent 

Per  cent 

Per  cent 

Per  cent 

650 

11.5 

45.1 

9.3 

30.5 

750 

6.1 

56.6 

17.5 

15.5 

900 

None 

41.6 

50.0 

5.0 

The  yields  of  gaseous  hydrocarbons  are  lower  than 
those  shown  in  Table  II,  which  were  obtained  at  the 
same  temperatures,  and  likewise  the  maximum  yield 
is  lower  than  the  maximum  obtained  under  atmospheric 
pressure. 

EFFECT    OF    DIMINISHED    PRESSURE     ON     GASEOUS    REAC- 
TIONS 

By  referring  to  the  OIL-GAS-TAR  system  cited 
above,  it  becomes  evident  that  a  high  vacuum  would 
favor  the  increase  in  volume  due  to  cracking  the  oil 
into  gas  and  at  the  same  time  withdraw  the  gas  from 

(33) 


200 


100- 


150- 
125 
100 
75 
50 
25 


10 


10 


Gas 


10  20  30  40 

Pressure      Ibs./sq.in. 


Carbon 


20 


30 


Tar 


20 


30 


CH4 


900°C. 


30 


40     Pres. 


40     Prcs. 


40     Pres. 


FIG.  VII — VARIATIONS  IN  YIELDS  of  PRODUCTS  AT  900°  C.,  UNDER  VARY- 
ING PRESSURES.     (TABLES  II,  III,  IV  AND  VI) 

(34) 


100 


50 


10 


10 


10 


10 


20 


30 


Ill 


20  30 


H 


20  30 


20 


30 


yoo°c. 


40      Pres. 


40     Pres. 


40     Pres. 


40     Pres. 


FIG.  VIII — VARIATIONS  IN  YIELDS  OF  PRODUCTS  AT  900°  C.,  UNDER  VARY- 
ING PRESSURES.     (TABLES  II,  III,  IV  AND  VI) 

(35) 


the  heat  zone  before  it  could  form  tar.  The  effects  of 
this  reduced  pressure  can  best  be  observed  from  the 
results  of  the  following  experiments:  » 


TABLE  IV 

Oil  used, 

400  cc. 

Temp. 

Pressure 

Gas 

Carbon 

"Tar" 

0  C. 

Absolute 

Liters 

Grams 

Cc. 

750 

1/20  to  1/30  atmos. 

146 

1 

153 

850 

1/20  to  1/30  atr 

nos. 

211 

3 

100 

900 

1/20  to  1/30  atr 

nos. 

234 

3 

60 

950 

1/20  to  1/30  atr 

nos. 

235 

12 

58 

Analysis  of  Gas  from  Table  IV 


Temp. 

C2H6 

CH4 

H2 

111 

°C. 

Per  cent 

Per  cent 

Per  cent 

Per  cent 

750 

.  .  . 

12.5 

56.1 

850 

3.4 

20.5 

15.6 

52.9 

900 

1.3 

24.0 

17.3 

52.1 

950 

Trace 

27.0 

20.8 

46.9 

This  striking  difference  in  end  products  due  to  di- 
minished pressure  seems  to  have  been  overlooked, 
perhaps  because  for  the  first  few  pounds  per  square 
inch  vacuum  the  increase  is  not  marked. 

INFLUENCE  OF  CONCENTRATION  CHANGES  ON  GASEOUS 
REACTIONS 

The  present  investigation  has  merely  opened  this 
field.  It  has  been  established  that  oil  cracked  in  an 
atmosphere  of  a  gas,  such  as  hydrogen,  which  reacts 
chemicalry  with  the  end  products  of  the  cracking 
process,  will  yield  products  which  are  not  analogous 
to  those  resulting  from  a  physical  mixture  of  the  two 
gases.  Not  only  does  the  mere  presence  of  the  ad- 
mixed gas  influence  the  end  products,  but  as  is  to  be 
expected  from  the  theoretical  consideration,  the  quan- 
tity of  the  admixed  gas  is  influential. 

To  study  the  various  gases  and  their  quantitative 
relation  will  require  much  further  experimental  work. 
The  results  of  preliminary  study  indicate  that  there  is  a 
vital  relationship  between  the  resulting  gases  in  a  crack- 
ing process  and  the  atmosphere  in  which  the  oil  is 
cracked.  This  relationship  is  likely  to  be  of  commer- 
cial significance  in  practical  water  gas  carburization. 
The  quantity  of  CO  and  H2  admixed  per  gallon  of 
oil  cracked  is  an  important  factor,  just  as  the  tempera- 
ture and  the  pressure  have  been  shown  to  be  impor- 
tant factors.  Jones,1  in  his  improved  all  oil  water 
gas  process,  recognizes  the  importance  of  adding  an 
11  active  gas"  to  the  cracking  zone,  but  considers 

1  The  Gas  Age,  1913,  p.  369;  American  Gas  Light  Journal,  1913,  p.  272; 
Gas  World,  1913,  916. 

(36) 


650* 


50* 


750* 


45*/n"Pres.- 
Abs. 


Temperature  in  Degrees  C. 


ATmos. 
Pres. 


750* 


8«0' 


Vacuum 


T. 


ILLUMINANTS 


FIG.  IX — PERCENTAGES  OF  ILLUMINANTS  UNDER  VARYING  TEMPERATURES 
AND  PRESSURES.     COMPILED  FROM  TABLES  II,  III  AND  IV 

(37) 


30- 


20- 


Abs, 


650' 


750* 


850°  <?00* 


40> 


20- 


Atmos. 
PPCS. 


650° 


750° 


850*  900° 


2 
2 120 

100 
80 
60 


Vacuum 


750* 


850" 


T. 


ILLUMINANTS 


FIG.  X — LITERS   OF   ILLUMINANTS   UNDER   VARYING    TEMPERATURES    AND 
PRESSURES.     COMPILED  FROM  TABLE  VI 

(38) 


the  effect  of  the  presence  of  the  admixed  gas  to  be 
catalytic.  Hempel1  found  that  by  cracking  oil  in  the 
presence  of  hydrogen  not  only  did  none  of  the  hydro- 
gen split  off  from  the  hydrocarbons,  but  part  of  the 
admixed  hydrogen  actually  combined  for  the  formation 
and  preservation  of  hydrocarbons.  On  the  other 
hand,  on  the  basis  of  a  single  experiment  reported, 
he  maintains  that  the  presence  of  CO  in  the  cracking 
zone  is  similar  to  the  presence  of  a  neutral  gas  and  is 
without  material  influence  on  the  end  products  ob- 
tained from  the  oil.  As  to  the  hydrogen,  the  results 
of  this  research  agree  with  the  observations  of  both 
Hempel  and  Jones.  The  quantity  and  quality  of 
gas  per  cc.  of  oil  increase,  and  qualitative  results  show 
that  the  tar  and  deposited  carbon  decrease. 

TABLE  V 
Pressure         Hz  Liters  Shrinkage 

Temp.  Absolute   admixed.     ' * •^      in  Hz. 

°C.          Lbs.  L.  C2H6  CH<  111  H2       Liters 

750  15.0  358          15.4          125.0  70.6          308          50 

800  15.0  412          18.0          116.0  83.2          335          77 

750  0.75  400  9.5            52.0  112.0  381  19 

810  0.75  413  86.5  140.0  378  35 

860  0.75  388  99.5  133.0  350  38 

900  0.75  292  92.0  120.0  272  •    20 

960  0.75  382  95.0  113.0  348  34 

From  these  results  it  appears  that  a  greater  per- 
centage of  the  admixed  hydrogen  enters  into  combina- 
tion to  form  saturated  hydrocarbons  when  the  crack- 
ing process  is  carried  out  under  atmospheric  pressure, 
than  is  the  case  under  greatly  reduced  pressure.  The 
percentage  increase  in  yield  of  the  illuminants  when 
the  cracking  process  is  carried  out  under  reduced 
pressure  in  the  presence  of  hydrogen  is  about  as  great, 
however,  as  is  the  percentage  increase  in  illuminants 
when  the  reaction  is  carried  out  under  atmospheric 
pressure. 

INFLUENCE    OF    TEMPERATURE,    PRESSURE    AND    CONCEN- 
TRATION    CHANGES     ON     COMPOSITION      OF     RE- 
SULTANT   TARS 

If  changing  temperature  and  pressure  have  a  marked 
influence  on  the  quantity  and  quality  of  gaseous  hydro- 
carbons obtained  from  cracking  petroleum  oil,  one 
should  expect  simultaneous  changes  in  the  condensa- 
ble hydrocarbons,  which  differ  from  the  permanent 
gaseous  hydrocarbons  only  in  that  they  are  liquid  or 
solid  at  ordinary  temperatures.  There  should  be  equi- 
librium between  all  hydrocarbons  of  a  series  at  the 

i  Jour.  f.  Gasb.,  1910,  p.  53,  et  al. 

(39) 


high  temperatures  prevailing  in  the  furnace  where 
practically  all  the  hydrocarbons  are  gaseous.  That 
the  end  products  should  contain  ethylene  and  then 
suddenly  jump  to  hexene  is  not  to  be  expected,  any 
more  than  that  the  hydrocarbons  in  coal  tar  would 
jump  from  benzene  to  naphthalene  or  anthracene. 
In  industrial  practice  the  "illuminants"  are  usually 
said  to  consist  of  75  per  cent  ethylene  and  25  per  cent 
benzene  vapor. 

When  the  gas  made  by  cracking  oil  in  the  apparatus 
under  one-thirtieth  of  an  atmosphere  pressure  abso- 
lute is  passed  over  palladium  in  the  presence  of  an 
excess  of  hydrogen,  over  90  per  cent  of  the  illuminants 
are  converted  into  saturated  hydrocarbons,  prin- 
cipally ethane,  indicating  that  the  illuminants  con- 
tain but  little,  if  any,  benzene  vapor.  If  the  gas  con- 
tains no  benzene,  it  is  only  logical  to  believe  that  the 
condensable  hydrocarbons  contain  no  aromatic  hydro- 
carbons. It  is  .further  found  that  the  vacuum  tar 
will  combine  with  1.82  sp.  gr.  sulfuric  acid.  It  has  a 
low  specific  gravity,  and  on  permitting  the  higher 
boiling  point  fractions  to  stand,  no  naphthalene  or 
anthracene  separate  out.  Tars  resulting  from  crack- 
ing oil  in  carbureting  blue  water  gas  under  atmos- 
pheric pressure  contain  quantities  of  benzene,  toluene 
and  other  aromatic  hydrocarbons  in  sufficient  amounts 
to  be  of  commercial  importance.  In  view  of  these 
facts,  there  is  justification  for  the  statement  that 
tars  which  result  from  cracking  petroleum  under 
low  pressures  are  different  from  those  which  result 
from  cracking  under  atmospheric  or  higher  pressure. 
Instead  of  benzene,  toluene  and  other  aromatic  hydro- 
carbons, the  vacuum  tar  contains  members  of  the  more 
unsaturated  hydrocarbon  series.  The  composition 
of  these  tars  is  now  the  subject  of  a  further  investiga- 
tion. 

SUMMARY 

In  the  theoretical  discussion  on  the  influence  of  dimin- 
ished pressure  on  oil  gas  manufacture,  it  was  pointed 
out  that  one  should  expect  an  increase  in  the  yield 
of  gaseous  hydrocarbons  from  a  given  amount  of  oil 
by  reducing  the  pressure  below  atmospheric.  This 
increase  should  reach  a  maximum  as  the  absolute  zero 
of  pressure  is  approached.  The  correctness  of  this  is 
shown  by  resultsrecordedin  Tables  IV  and  VI.  Not  only 
are  the  gaseous  hydrocarbons  yields  greatly  increased, 
but  the  deposited  carbon  is  practically  eliminated, 

(40) 


and  there  is  much  less  gaseous  hydrogen  produced 
than  in  the  product  obtained  at  the  same  tempera- 
tures under  higher  pressure. 

It  was  pointed  out  that  increasing  the  total  pressure 
under  which  the  oil  is  cracked  to  several  atmospheres 
will  decrease  the  gaseous  hydrocarbon  yields  from  a 
given  amount  of  oil.  Experimental  results,  shown 
in  Table  III,  have  proven  this  correct. 

It  was  pointed  out  that  varying  the  pressure  on  the 
system  would  enable  one  to  better  control  the  quan- 
tity .and  quality  of  "tar"  obtained  than  at  present 
where  all  tar  is  made  under  atmospheric  pressure. 
Experimental  results  indicate  considerable  flexibility. 

It  has  further  been  established  that  the  end  prod- 
ucts resulting  from  cracking  oil  in  an  atmosphere  of  a 
gas,  such  as  H2,  which  reacts  chemically  with  the  end 
products  of  the  cracking,  are  a  function  of  both  the 
composition  and  the  quantity  of  the  gas  admixed, 
per  Table  V. 

Experiments,  Table  IV,  have  proven  that  it  is  possi- 
ble to  "crack"  oil  at  a  temperature  of  900°  C.  with- 
out depositing  more  carbon  than  i%  by  weight  of  the 
oil  used. 

TABLE  VI — SUMMARY  OF  GAS  TABLES 

(All  based  on  400  cc.  oil  and  calculated  to  0°  C.,  and  760  mm.  pressure) 

Pressure 

Temp.    Lbs.  per  Gas     Carbon      Tar      C2H6          CH<            H2  111 

0  C.        sq.  in         L.           G.          Cc.          L.               L.              L.  L. 

Atmospheric  Pressure  Group  (See  Table  II) 

650         15.0          135              3        163        13.8            45.5           12.1  58.8 

750         15.0          206            18          80        10.15          84.5          39.6  63.0 

900         15.0          382          115          11        Trace        178.1        148.2  50.0 

High  Pressure  Group  (See  Table  III) 

650        45.0          145              8        133        16.7            65.2  13.1  44.3 

750        45.0          194            26          87        11.8          110.0  33.9  30.1 

900        45.0          310          165            9        None         128.9  155.0  15.5 

Low  Pressure  Group  (See  Tables  I  and  IV) 

750           0.75        146               1        153             ..                ..             18.3  82.0 

850           0.75        211               3        100          7.16          43.2          32.9  111.5 

900           0.75        234              3          60          3.0            56.0          40.0  122.0 

950           0.75        235             12          58       Trace          63.4          48.8  110.0 

Admixed  Gas  Group  (See  Table  V) 


Hydrogen 
admixed 
L. 
750         15.0         358 

Hydrogen 
shrinkage 
L. 
50        15.4 

125.0 

308.0 

70.6 

800         15.0 

412 

77        18.0 

116.0 

335.0 

83.2 

750 

.0 

400 

19          9.5 

52.0 

381.0 

112.0 

810 

.0 

413 

35 

86.5 

378.0 

140.0 

860 

.0 

388 

38 

99.5 

350.0 

133.0 

900 

.0 

292 

20 

92.0 

272.0 

120.0 

950 

.0 

382 

34 

95.0 

348  .  0 

113.0 

(41) 


Through  a  proper  consideration  of  equilibrium  and 
mass  action  conditions  under  various  degrees  of  tem- 
perature and  pressure,  much  can  be  expected  in  gaseous 
reactions.  It  soon  becomes  evident  that  the  single 
stage  method  wherein  endothermic  and  exothermic, 
expansion  and  contraction  reactions  are  combined  in 
a  single  apparatus,  is  open  to  question. 


(42) 


VITA 

Walter  Frank  Rittman  was  born  in  Sandusky, 
Ohio,  on  December  2,  1883.  Before  entering  col- 
lege he  spent  four  years  in  the  shops  and  drawing  rooms 
of  steel  and  machine  manufacturers  in  Cleveland, 
Ohio.  He  received  the  degrees  of  A.B.  from  Swarth- 
more  College  in  1908,  M.A.  in  1909,  and  M.E.  in 
1911.  During  1909  he  served  as  chemist  in  the  lab- 
oratory of  the  United  Gas  Improvement  Company,  of 
Philadelphia.  From  1909  to  1912  he  was  engaged  in 
professional  chemical  engineering  work  in  and  about 
Philadelphia,  and  at  the  same  time  held  the  position 
of  lecturer  and  laboratory  instructor  in  Industrial 
Chemistry  at  Swarthmore  College.  From  1912  to 
1914  he  was  engaged  in  graduate  study  in  Columbia 
University.  He  was  special  lecturer  on  Industrial 
Chemistry  at  Columbia  University  in  the  Summer 
School  of  1913. 


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